1. Field of the Invention
The present invention is directed to a process of producing glass fiber light conductors.
2. Prior Art
Normally glass fiber light conductors, which have a low attenuating effect, consist of a cylindrical quartz glass core having an index of refraction n.sub.K, which core is surrounded by a quartz glass casing or cladding having an index of refraction n.sub.M, where n.sub.M is smaller or less than n.sub.K. The desired difference of the index of refraction can be set by utilizing different amounts of doping material in the core glass and the cladding glass, which doping materials are suitable oxides. Light conducting fibers of this type are generally produced in accordance with a chemical vapor deposition process (a CVD method), for example, by depositing the oxides from a gas phase in a glass tube which is subsequently collapsed.
Although these glass fiber light conductors have outstanding light transmittancy, their practical use is limited by their low tensile strength. Under special conditions in a vacuum, a high tensile strength can, in fact, be measured on the quartz glass fiber. Glass fiber light conductors, which are exposed to the atmosphere, rapidly loose their tensile strength when handled. The supposition is that the fiber breakage is due to irregular, mechanical damage to the surface of the fiber.
In order to increase the tensile strength, the glass fiber light conductor is provided with a thin layer of synthetic material immediately following the drawing process of the fiber. This provides a conductor with a certain protection against environmental influences such as corrosion, mechanical damage due to contact and, therefore, improves the stability of the fiber. Before a light conductor of this type can be used in practice, it must be joined in a cable to enable it to withstand the tensile forces which will occur when a cable is installed. The speed and costs involved in a process of forming a cable are basically dependent upon the stability of the light conductor fiber.